1. Field
One or more embodiments of the present invention relate to a distance measurement method, medium, and apparatus and, more particularly, to a distance measurement method, medium, and apparatus for applying light to a target object and measuring a distance between the distance measurement apparatus and the target object using a round trip time including the time it takes for the light to be irradiated to the target object and then reflected from the target object.
2. Description of the Related Art
To measure a distance between a distance measurement apparatus and a target object, a method of irradiating light to the target object, measuring a round trip time including the time it takes for the light to be irradiated to the target object and then reflected from the target object, and calculating the distance between the distance measurement apparatus and the target object using the round trip time is generally used. In this case, the distance is calculated by dividing the round trip time by 2 to obtain an arrival time required for the light to arrive at the target object and multiplying the arrival time by the velocity of light. Here, the velocity of light is a constant, that is, 3×108 m/s, and thus it is very important to measure the round trip time with accuracy in order to calculate the correct distance.
The round trip time can be calculated using a phase difference between the light irradiated at the target object and the light reflected from the object, which is disclosed in an article entitled “Solid-State Time-of-Flight Range Camera” by Robert Lange and Peter Seits, appearing in IEEE Journal of quantum electronics, Vol. 37, No. 3, pp. 390-397, March 2001. However, this method of calculating a round trip time of light using the phase difference cannot measure a correct round trip time for an object located at a distance at which the phase difference is greater than 360° because the phase difference is repeated in the cycle of 360°.
According to U.S. Patent Application No. 2006-353229, a round trip time of light is measured using a time to digital converter (TDC), and thus a distance between a distance measurement apparatus and an object is not limited. The TDC counts pulses of a pulse signal during a period from when light is irradiated to the object to when the light is reflected from the object to measure the round trip time of the light. However, to measure a correct round trip time, a very short pulse width is required, and thus the pulse signal must have a very high frequency. For example, a pulse signal having a frequency of hundreds of GHz is required for accuracy of 1 mm. That is, a TDC using a high-frequency pulse signal is needed to increase the accuracy of distance measurement, and thus high power is required.